Interleukin-1 (IL-1) is a potent inflammatory cytokine and is a key mediator in many diseases and medical conditions. IL-1 activity is mediated by IL-1α and IL-1β, which are related polypeptides, both of which bind the IL-1 type 1 receptor (IL-1R1) and are expressed by many cells, including those of the macrophage/monocyte lineage. IL-1 stimulates cellular responses by interacting with a heterodimeric receptor complex comprised of two transmembrane proteins, IL-1R1 and IL-1 receptor accessory protein (IL-1RAcP). IL-1 forms a complex with IL-1R1, which recruits IL-1RAcP (Greenfeder et al., 1995, J. Biol. Chem. 270:13757–13765; Yoon and Dinarello, 1998, J. Immunology 160:3170–3179; Cullinan et al., 1998, J. Immunology 161:5614–5620). Cell-based binding studies suggest that IL-1RAcP stabilizes the IL-1R1 signaling complex by slowing the ligand off-rate (Wesche et al., 1998, FEBS Letters 429:303–306). IL-1RAcP has no significant affinity for either IL-1 or IL-1R1 alone, but high affinity for the IL-1:IL-1R1 complex (Ettorre et al., 1997, Eur. Cytokine Netw. 8:161–171).
The IL-1 receptor antagonist (IL-1ra) competes with IL-1α and β for receptor binding but fails to recruit IL-1RAcP, resulting in an occupied but non-signaling receptor. IL-1 activity is also regulated by IL-1 type 2 receptor (IL-1R2), which is a decoy receptor that binds ligand but does not participate in signaling due to a truncated intracellular domain. IL-1ra and IL-1R2 reduce the severity and duration of IL-1 mediated inflammatory events by inhibiting IL-1 signaling (Wesche et al., 1998, FEBS Letters 429:303–306; Dripps et al., 1991, J. Biol. Chem. 266:10331–10336; Dripps et al., 1991, J. Biol. Chem. 266:20331–20335).
IL-1 inhibitors may block IL-1 activity by down-regulating IL-1 expression, binding free IL-1, interfering with IL-1 binding to its receptor, interfering with formation of the IL-1 receptor complex (i.e., association of IL-1 receptor with IL-1 receptor accessory protein), or interfering with modulation of IL-1 signaling after binding to its receptor. Several classes of interleukin-1 inhibitors are known, including interleukin-1 receptor antagonists such as IL-1ra, anti-IL-1 receptor monoclonal antibodies (e.g., EP 623674), the disclosure of which is hereby incorporated by reference, IL-1 binding proteins such as soluble IL-1 receptors (e.g., U.S. Pat. No. 5,492,888, U.S. Pat. No. 5,488,032, and U.S. Pat. No. 5,464,937, U.S. Pat. No. 5,319,071, and U.S. Pat. No. 5,180,812, the disclosures of which are hereby incorporated by reference), anti-IL-1 monoclonal antibodies (e.g., WO 95/01997, WO 94/02627, WO 90/06371, U.S. Pat. No. 4,935,343, EP 364778, EP 267611 and EP 220063, the disclosures of which are hereby incorporated by reference), IL-1 receptor accessory proteins and antibodies thereto (e.g., WO 96/23067 and WO 99/37773, the disclosures of which are hereby incorporated by reference), inhibitors of IL-1β converting enzyme (ICE) or caspase I (e.g., WO 99/46248, WO 99/47545, and WO 99/47154, the disclosures of which are hereby incorporated by reference), which can be used to inhibit IL-1β production and secretion, IL-1β protease inhibitors, and other compounds and proteins which block in vivo synthesis or extracellular release of IL-1.
Exemplary IL-1 inhibitors are disclosed in the following references: U.S. Pat. Nos. 5,747,444; 5,359,032; 5,608,035; 5,843,905; 5,359,032; 5,866,576; 5,869,660; 5,869,315; 5,872,095; 5,955,480; 5,965,564; International (WO) patent applications 98/21957, 96/09323, 91/17184, 96/40907, 98/32733, 98/42325, 98/44940, 98/47892, 98/56377, 99/03837, 99/06426, 99/06042, 91/17249, 98/32733, 98/17661, 97/08174, 95/34326, 99/36426, 99/36415; European (EP) patent applications 534978 and 89479; French patent application FR 2762514. The disclosures of all of the aforementioned references are hereby incorporated by reference.
Several IL-1 receptor antagonist peptides have been identified from phage-display libraries, including a 21-mer IL-1 antagonist peptide (AF10847) with an IC50 of 2.6 nM and a tetra-peptoid (referred to herein as 3891—11a) with an IC50 of 6.7 μM (WO 96/29088, the disclosure of which is hereby incorporated by reference). The chemical structure of 389—11a is shown in FIG. 1. These molecules appear to be pure receptor antagonists, like IL-1ra.
The three-dimensional structures of IL-1ra (Vigers et al., 1994, J. Biol. Chem. 269:12874–12879) and IL-1β (von Oostrum, 1991, J. Struct. Biol. 107:189) have been elucidated using X-ray crystallography. A construct expressing the extracellular portion of IL-1R1 (IL-1R1_EC) was used by Vigers et al. to solve co-crystal structures of the IL-1R1_EC:IL-1β complex (Vigers et al., 1997, Nature 386:190–194) and IL-1R1_EC:AF10847 complex (Vigers et al., 2000, J. Biol. Chem. 275:36927–36933). A similar method was used to solve the structure of IL-1R1_EC:IL-1Ra (Shreuder et al., 1997, Nature 386:194–200). These studies indicate that IL-1R1_EC contains three immunoglobulin-like (Ig-like) domains. The first two Ig-like domains of IL-1R1_EC are tightly linked, while the third domain is attached by a flexible linker. IL-1β (and presumably IL-1α) binds to IL-1R1 at two sites. The first site (Site A) is at the junction of the first and second Ig-like domains, and the second site (Site B) is on the face of the third domain. Most of the interactions for IL-1ra and AF10847 are located at site A while the third Ig-like domain does not contribute substantially to the binding affinity (Vigers et al., 2000, J. Biol. Chem. 275:36927–36933).
Small molecules with conventional drug-like characteristics that bind IL-1R1 and inhibit IL-1 activity are of great therapeutic interest. There is a need in the art for effective small molecule inhibitors of the IL-1 signaling pathway that may ameliorate the effects of IL-1 mediated diseases. Particularly, there is a need for clinically relevant small molecule inhibitors that are suitable for delivery into human patients.